The objective of this study is to determine whether direct aspiration of enlarged parathyroid glands under CT or ultrasound control can replace selective venous sampling and PTH assay as a localizing technique. Selective venous sampling is tedious, time-consuming, and involves significant radiation to both patient and angiographer. An elevation of parathyroid hormone in a selective vein localizes the general site of the adenoma but does not pinpoint it for easy surgical excision. An increasing number of parathyroid adenomas have been identified in the neck and upper portions of the mediastinum both at CT scanning and ultrasound. Despite bolus injections, distinguishing these soft tissue densities from vascular or thymic structures remains a problem. Under either CT or ultrasono- graphic control, a skinny needle can generally be introduced into these glands and minute amounts of tissue juices aspirated. Significance of Research: The ability to localize parathyroid tissue with a combination of CT or ultrasound and direct aspiration would greatly simplify parathyroid localizations, eliminating both the arteriographic study, which has significant risk, and the venous sampling.